The present invention relates to an Erysimum cheiri (also called wallflower) seed, an Erysimum cheiri plant, Erysimum cheiri varieties and Erysimum cheiri hybrids, which contain one or more male sterility alleles. This invention further relates to a method for producing Erysimum cheiri (F1) hybrid seed and plants.
The wallflower is a popular spring and early summer bedding plant in the United Kingdom and Northern Europe and a number of different varieties are widely available. It originates from a wild flower, growing on walls, cliffs and rocks in Greece and the Aegean. English wallflower grows best in full sun or light shade and in a well-drained soil. The plants exhibit a full range of flower colors including white, yellow, red, orange, purple and intermediates. The plant is a biennial in cold climates, in warm climates it is a short-lived perennial. Most varieties are 12 to 30 inches tall and usually have fragrant flowers. Some winter protection is needed in colder climates.
Field crops including ornamentals, are bred and produced through methods that take advantage of the plant's method of pollination. Cross-pollinated crops, including all existing commercial varieties of Erysimum cheiri, rely on the ability of a flower to transfer functional pollen from its anthers to its stigma, thus resulting in formation of seeds. A true breeding line can be produced by successive self-pollination of a selected plant. Repeated selfing or inbreeding, however, results in genetic weakness, variously described as inbreeding depression. Vigor can be restored to true breeding lines by intercrossing in isolation, resulting in uniform progenies that can be marketed as uniform open pollinated cultivars.
Alternatives to the open-pollinated Erysimum cheiri varieties are F1 hybrids. In F1 hybrid varieties, pollen from an inbred “male” line is used to pollinate an inbred, but genetically different “female” line. The resulting F1 hybrids are both phenotypically uniform and vigorous. In addition to this hybrid vigor, hybrids also offer opportunities for the rapid and controlled deployment of dominant genes for resistance to diseases and pests. A homozygous dominant gene in one parent of a hybrid will result in all F1 hybrids expressing the dominant gene phenotype.
Much progress has been made in the improvement of horticultural and agronomic crops over the past several decades. Prominent among the methods used has been that of F1 hybrid seed production. Essentially all corn, tomato, cucumber, and vegetable crops in general, are grown from F1 hybrid seed. Ornamentals including petunias, geraniums, impatiens, snapdragons, and many others are grown as F1 hybrids. Within the seed trade industry, F1 hybrids command the preeminent role because of their superior vigor, uniformity and performance.
Male sterility, both naturally occurring and artificially induced, is a means of achieving controlled hybridization by the prevention of self-pollination in plants, aside from manual emasculation. In male sterility (ms) systems, absence of pollen in normally hermaphroditic flowers precludes the possibility that flowers will pollinate themselves. Without access to pollen, sexual fusion of the male and female gametes that would normally lead to seed development does not occur; the end consequence is that no “self” seed (i.e. seed arising from self-pollinations) is produced.
In higher plants, two major types of male sterility can be distinguished according to their genetic control. Genetic male sterility (GMS), sometimes referred to as genic, nuclear, or Mendelian sterility is controlled by genes carried and expressed within the nucleus of cells. Inheritance of genetic male sterility typically follows normal Mendelian segregation patterns. In contrast, cytoplasmic male sterility (CMS) is governed by cytoplasmic factors, principally the mitochondrial genome; inheritance of cytoplasmic male sterility does not follow Mendelian patterns and instead, is associated with maternal transmission of mitochondrial components from generation to generation. Neither GMS or CMS is known to occur in any Erysimum species, but GMS is known to occur naturally elsewhere in the Cruciferae family (Tsunoda S, Hinata K, and Gomez-Campo C (1980) Brassica Crops and Wild Allies. Japan Scientific Societies Press).
Open-pollination is an important and universal component of the reproductive biology of wallflower species. For effective commercial production of F1 hybrid Erysimum cheiri cultivars the use of male sterility genes would be valuable.